1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a method of fabricating a liquid crystal display (LCD) device.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, many efforts and studies are being made to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
FIG. 1 is a perspective view illustrating an LCD device according to the related art. Referring to FIG. 1, the LCD device 3 includes an array substrate 22, a color filter substrate 5, and a liquid crystal layer 11 between the two substrates.
The array substrate 22 includes gate lines 12 and data lines 24 crossing each other to define a pixel region P on a first substrate 22. A thin film transistor T is located at a crossing of gate line 12 and data line 24. The thin film transistor T includes a gate electrode 30, a semiconductor layer 32, a source electrode 34, and a drain electrode 36. A pixel electrode 17 is disposed in the pixel region P and connected to the drain electrode 36.
The color filter substrate 5 includes red (R), green (G), and blue (B) color filter patterns 7a, 7b, and 7c in respective pixel regions P and a black matrix 6 between the color filter patterns. 7a, 7b, and 7c, on the color filter substrate 5. A common electrode 9 is disposed on the color filter patterns 7a, 7b, and 7c. 
When voltages are applied to the pixel electrode 17 and common electrode 9, an electric field is induced. The liquid crystal molecules are arranged by the induced electric field, and the light transmissivity of the LCD device 3 is changed. Thus, images are displayed.
The thin film transistors may have various types, for example, an inverted staggered type. FIG. 2 is a cross-sectional view illustrating an LCD device having an inverted staggered type thin film transistor according to the related art. Referring to FIG. 2, the inverted staggered type thin film transistor T includes a gate electrode 52 on a substrate 50, a semiconductor layer 56 over the gate electrode 52, and source and drain electrodes 60 and 62 on the semiconductor layer 56. The semiconductor layer 56 has an active layer 57 and an ohmic contact layer 58. A passivation layer 64 is on the thin film transistor T, and a pixel electrode 68 is on the passivation layer 64 such that the pixel electrode 68 contacts the drain electrode 62 through a drain contact hole 66.
FIGS. 3A to 3E are cross-sectional views illustrating a method of fabricating an array substrate having an inverted staggered type thin film transistor according to the related art. Referring to FIG. 3A, a metallic material is deposited on a substrate 50 and patterned to form a gate electrode 52 and a gate line (not shown). A gate insulating layer 54 is formed on the substrate 50 having the gate electrode 52. Referring to FIG. 3B, an intrinsic amorphous silicon layer and an impurity-doped amorphous silicon layer are formed on the gate insulating layer 54 and patterned to form an active layer 57 and an ohmic contact layer 58. Referring to FIG. 3C, a metallic material is deposited on the substrate 50 having the active layer 57 and the ohmic contact layer 58 and patterned to form source electrode 60 and drain electrode 62, and a data line (not shown). A portion of the ohmic contact layer 58 exposed between the source and drain electrodes 60 and 62 is removed and a portion of the active layer 57 (i.e., a channel portion ) is exposed. Referring to FIG. 3D, a passivation layer 64 is formed on the substrate 50 having the source and drain electrodes 60 and 62. The passivation layer 64 is patterned to form a drain contact hole 66 exposing the drain electrode 62. Referring to FIG. 3E, a transparent conductive layer is formed on the passivation layer 64 and patterned to form a pixel electrode 68 contacting the drain electrode 62.
As described above, the gate electrode 52 and the gate line (not shown) are formed in a first mask process, the active layer 57 and the ohmic contact layer 58 are formed in a second mask process, the source and drain electrodes 60 and 62 and the data line (not shown) are formed in a third mask process, the passivation layer 64 having the drain contact hole 66 is formed in a fourth mask process, and the pixel electrode 68 is formed in a fifth mask process. Through the above five mask processes, the array substrate 22 is fabricated.
In each of the above mask processes, processes of forming a layer on a substrate in a chamber, forming a photoresist layer on the layer, light-exposing the photoresist layer using a mask, and stripping the photoresist layer to form a photoresist pattern, etching the layer using the photoresist pattern, cleaning the substrate, and so on are conducted.
After the process of forming the layer in the chamber, the substrate may come out of the chamber for the other processes and be exposed to an external condition. When the substrate is exposed, an exposed portion of the substrate may be contaminated by external particles. In particular, when the channel portion is exposed and contaminated, leakage current may be caused through a contaminated surface of the channel portion. Accordingly, the thin film transistor operates abnormally to cause blurring, and reliability is reduced.